Antisense Inhibition of Photosynthetic Carbon Fixation Enzymes

Abstract

The photosynthetic capacity of a leaf might be regulated by the activity of various enzymes

of the Calvin cycle. The antisense inhibition of specific enzymes in Calvin cycle have

provided important tools to understand metabolic regulation of the cycle. The analysis

carried out on the sedoheptulose-l,7-bisphosphatase antisense plants indicated that even

35% reduction in the ezymes activity was enough to reduce photosynthetic carbon

assimilation. In contrast to these results, transgenic plants with reduced levels of ribulose-

1,5- biphosphatase/oxygenase, fruktose-l,6-bisphosphatase, phosphoribulokinase and

glyceraldehyde-3- phosphate dehydrogenase, reductions of between 65% and 90% in the

activities of these enzymes were required before any effect on photosynthetic carbon

assimilation was observed. Also antisense inhibition of all Calvin cycle enzymes resulted in

reduced starch level while sucrose level was maintained. However, it was shown that

changes in photosynthesis was depend on the environmental conditions and short or long

term experimental sudies.

Keywords

• Antisense,Calvin cycle,transgenic plants

FOTOSENTETİK KARBON FİKSASYONUNDA ROL ALAN ENZİMLERİN ANTİSENSE İNHİBİSYONU

Abstract

Bir yapraktaki fotosentetik aktivite Calvin döngüsü içindeki çeşitli enzimlerin aktivitesi

tarafından regüle edilebilir. Calvin döngüsü içindeki spesifik enzimlerin antisense

inhibisyonu, bu döngünün metabolik regülasyonunun anlaşılması için önemli ip uçları

vermektedir. Sedoheptulose-l,7-bifosfataz antisense bitkileri üzerinde yapılan analizler, bu

enzimin aktivitesindeki %35’ lik bir düşüşün bile fotosentetik karbon asimilasyonunun

azalması için yeterli olduğunu göstermiştir. Bu sonuçlara karşıt olarak, indirgenmiş ribuloz-

1,5 bifosfataz/oksijenaz, fruktoz-l,6-bifosfataz, fosforibulokinaz ve gliseraldehit-3-fosfat

dehidrogenaz aktivitelerine sahip transgenik bitkilerde ise, fotosentetik karbon

asimilasyonunda herhangi bir etki görülmesi için bu enzimlerin aktivitelerinde %65 ve %90

arasında bir azalmaya gereksinim olduğu bulunmuştur. Ayrıca tüm antisense bitkilerde

Calvin döngüsü enzimlerinin inhibisyonu nişasta miktarını düşürürken sukroz miktarında

önemli değişimler kaydedilmemiştir. Fakat fotosentezde görülen bu değişimin bitkinin

büyüme ortamına veya kısa ya da uzun süreli deney ortamına bağlı olarak değiştiği

saptanmıştır.

Keywords

• Antisense,Calvin döngüsü,transgenik bitkiler

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